The present invention generally relates to prosthodontic casts, and more particularly to an improvement in the pins and sleeves which permit the separation and simple replacement in original positions of the segments on a base cast.
Prosthodontics denote that branch of the dental art or science that specifically treats the replacement of missing dental and oral tissues. The basic art of dental prosthodontics is well known. Many specialized procedures have been worked out for making crowns, inlays, bridge work and the like. In this type of work, it is customary to make an impression in rubber or a similar material by making an impression in a tray. The tray is generally filled with a suitable impression material, such as wax, hydrocolloid and the like. The dental impression tray, with the impression material therein, is placed in the patient's mouth and results in a negative impresssion of the tooth or teeth upon which the work is to be performed. The hardened dye is generally provided on the underside with dowel pins that are used in a base so that the die may be separated from the base and removed therefrom to facilitate working thereon. The setting of the dowel pins both relative to the die and to each other is extremely important if the segments, which are to be removed for closer scrutiny, are to be replaced in proper alignment. It frequently happens that the work is to be performed on only one or a group of teeth at a time. By making it possible to remove small segments from the overall die or cast, the work is facilitated to a great extent.
Various pins and bushings are already known in the prior art. However, most of the known pins have disadvantages which have limited their usefulness. Thus, for example, according to one known pin design, all the pins are of the same length and extend equal distances above the surface in which they are embedded. Such an arrangement is disclosed in U.S. Pat. No. 3,704,519. This pin design has the disadvantage that when it is desired to replace a segment on the cast, it is difficult to align the two or more pins simultaneously before the pins may be inserted into the corresponding bushings.
According to another pin design, the free extending ends of the pins are cylindrical and of uniform diameter. This design has the disadvantage that the pins must be perfectly centered with respect to the openings of the bushings before insertion can be achieved. In both cases, replacement of segments is inconvenient and time consuming.
A still further disadvantage of many of the prior art prosthodontic casts arrangements is that the base cast onto which the segments are mounted is frequently substantially thicker than the length of the pins which they receive. Consequently, the pins do not fully extend through the base cast and the pins are accessible therethrough when the segments are mounted on the base cast. This has the disadvantage that the pins cannot be externally reached for applying pressure thereon and removing a segment when the pins become stuck within the openings in the base cast. Consequently, application of forces directly to the dental model casts may damage or break the same when the pins are frozen within their associated apertures or holes.